Integrated circuit and method for controlling a power supply thereof

ABSTRACT

Integrated circuit ( 1 ), which is supplied externally by a supply voltage (VDD), having at least one useful circuit ( 2 ) and a power supply for the at least one useful circuit which comprises a plurality of power supply units ( 3; 17   a,    17   b ), in which case the power supply comprises a control unit ( 18 ) for comparing the supply voltage (VDD) with a predetermined desired value and for switching one or a plurality of the switchable power supply units ( 17   b ) on or off in a manner dependent on the comparison result.

[0001] The invention relates to an integrated circuit according to the preamble of claim 1 and to a method for controlling a power supply for such an integrated circuit according to the preamble of claim 5.

[0002] Present-day microelectronic circuits use voltage generators on chip in order to generate a stable, defined voltage from the external supply voltage. Although the external supply voltage is predetermined, it can fluctuate within the specification limits.

[0003] A typical example is the generation of an internal voltage of 2.0 V from an external supply voltage of 2.5±0.2 V. For this purpose, a plurality of voltage generators are distributed over the chip. In this case, each of the plurality of voltage generators usually comprises a pFET or nFET transistor (pull-up transistor) and a comparator. The comparator is connected via an input to a stable reference voltage, which is generally generated by a bandgap reference circuit.

[0004] Particularly in the event of small differences between the supply voltage and the internal voltage, the problem arises, however, that the number of voltage generators used on the chip has to become very large. Since these voltage generators themselves require an operating current that is not small, a significant increase in the total operating current may thus result. At the present time, the number of voltage generators is chosen such that the internal voltage can still be generated even at the lowest permissible supply voltage. Moreover, for safeguarding purposes, further generators over and above this are also included in the design.

[0005] It is an object of the present invention to optimize the number of generators which are actually in use in a manner dependent on the operating conditions.

[0006] This object is achieved by means of an integrated circuit according to claim 1 and a method according to claim 5. The subclaims relate to preferred embodiments of the invention.

[0007] The way in which the above object is achieved according to the invention consists in the power supply units being connected in or disconnected in a manner dependent on the external voltage. Within the framework prescribed by the specification, a check is made to determine whether or not the external supply voltage lies above a predetermined desired value. If the external supply voltage lies above the desired value, the minimum number of power supply units is activated which suffices to generate the internal voltage from the higher supply voltage. Otherwise, additional generators are activated.

[0008] According to the invention, the integrated circuit, which is supplied externally by a supply voltage, having at least one useful circuit and a power supply for the at least one useful circuit which comprises a plurality of power supply units, is characterized in that the power supply comprises a control unit for comparing the supply voltage with a predetermined desired value and for switching one or a plurality of the switchable power supply units on or off in a manner dependent on the comparison result.

[0009] Preferably, the control unit comprises a low-current comparator for comparing the supply voltage with the predetermined desired value. In particular, the low-current comparator comprises a voltage divider between an operating voltage and ground in order to generate the desired value.

[0010] Preferably, the reference voltage is generated by a bandgap reference circuit.

[0011] According to the invention, the method for controlling a power supply for such an integrated circuit is characterized by the following steps: comparison of the supply voltage with a predetermined desired value and switching of one or a plurality of the switchable power supply units on or off in a manner dependent on the comparison result by a control unit.

[0012] Preferably, the comparison of the supply voltage is carried out stepwise with a plurality of predetermined desired values, so that the switchable power supply units are connected in a staggered manner.

[0013] In particular, the switchable power supply units are switched on and off with a hysteresis, thereby preventing oscillations.

[0014] One advantage of the solution according to the invention is that the control unit is relatively simple in its construction and therefore takes up little space on the chip.

[0015] Further features and advantages of the invention emerge from the following description of preferred exemplary embodiments, in which reference is made to the accompanying drawings.

[0016]FIG. 1 shows a traditional integrated circuit having a useful circuit and a plurality of power supply units.

[0017]FIG. 2 shows a typical construction of a power supply unit.

[0018]FIG. 3 shows the construction of the comparator in the power supply unit according to FIG. 2.

[0019]FIG. 4 shows an embodiment of the control unit according to the invention.

[0020]FIG. 1 illustrates an integrated circuit 1 on a chip, which has a useful circuit 2. The useful circuit 2 is supplied by a power supply integrated on the chip. The power supply is composed of a plurality of power supply units 3. The latter are distributed on the chip of the integrated circuit around the useful circuit 2, so that the lines 4 via which they are connected to the essential loads of the useful circuit 2 are as short as possible.

[0021] For their part, the power supply units 3 are connected to external supply lines 5 and 6, of which, by way of example, one is at the supply potential VDD and the other is grounded.

[0022]FIG. 2 illustrates a typical power supply unit 3. It comprises an actual generator circuit 7, which in turn essentially has a driver stage 8 driven by a comparator 9. The driver stage 8, which is illustrated here as a pFET transistor, is connected between the (external) supply voltage VDD and ground. The source of the driver transistor 8 is connected to VDD and its gate is connected to the output OUT of the comparator 9. The internal supply voltage VINT is tapped off at its drain, which is grounded via a voltage divider 10 a, 10 b.

[0023] The first input of the comparator 9 (its noninverting input) is connected to the center tap of the voltage divider 10 a, 10 b. A reference voltage is present at the second (inverting) input of the comparator 9, said reference voltage being produced by a bandgap reference circuit 11 in the circuit illustrated. The bandgap reference circuit 11 is generally not part of the actual generator circuit 7; it is present only once on the chip and serves as reference voltage source for a plurality of different circuits.

[0024] The power supply unit 7 can be activated or brought to a quiescent state via one or a plurality of switching elements 12 a and 12 b.

[0025]FIG. 3 shows the construction of the comparator 9 in FIG. 2. It is a differential amplifier having a first nFET input transistor 13 a at the noninverting input and a second nFET input transistor 13 b at the inverting input. By way of example, the voltage which is dropped across the second resistor 10 b of the voltage divider in FIG. 2 is present at the first transistor 13 a. In this case, the voltage supplied by the bandgap reference circuit 11 is present at the second transistor 13 b.

[0026] The source of the first input transistor 13 a is connected to VDD via a first pFET transistor 14 a, connected as a diode. The source of the second input transistor 13 b is likewise connected to VDD via a pFET transistor 14 b. The signal OUT for driving the driver transistor 8 is tapped off at the source of the second transistor 13 b. The drain of the two transistors 13 a and 13 b is connected to a current source. The current source in the drain circuit of the two input transistors 13 a and 13 b is in this case illustrated as an nFET transistor 15. The connection of the drain of the two transistors 13 a and 13 b to the current source 15 can be interrupted by a switching element 16, at whose input an ENABLE signal is present.

[0027] According to the invention, the ENABLE inputs of the circuits described above are used to selectively activate the circuits, or put them into a quiescent state, by means of a central control. FIG. 4 shows an embodiment of the power supply of an integrated circuit having a useful circuit (not illustrated) and a plurality of power supply units, two of which are illustrated, namely 17 a and 17 b. Both power supply units 17 a and 17 b refer to a bandgap reference circuit 11. They each have an ENABLE input via which they can be activated in the manner described above in connection with FIG. 2 and FIG. 3.

[0028] In the illustration in FIG. 4, the ENABLE input of the power supply unit 17 a is not connected, so that it is permanently active. (It goes without saying, however, that the ENABLE input of the power supply 17 a can also be routed to the outside, so that the power supply 17 a can be switched on or off in a manner dependent on conditions that are not considered any further here.) By contrast, the power supply 17 b is driven via its ENABLE input by a control unit 18. The control unit 18 comprises a low-current comparator 19, which compares the bandgap reference voltage with the actual supply voltage VDD that is applied externally. In practice, the low-current comparator 19 compares the bandgap reference voltage with a predetermined fraction of the external supply voltage VDD, which can be set very precisely by means of voltage dividers 20 a, 20 b. If said fraction of the external supply voltage VDD falls below the bandgap reference voltage of the circuit 11, i.e. below the desired value, a signal is output to the ENABLE input of the second power supply unit 17 b, so that the latter is activated. By contrast, if the bandgap reference voltage of the circuit 11 falls below the fraction of the external supply voltage VDD, a signal is correspondingly output to the ENABLE input of the second power supply unit 17 b, which signal causes the second power supply unit 17 b to be disconnected.

[0029] It is thus ensured that, in a manner dependent on the magnitude of the external supply voltage, only as many power supply units 17 b are switched on as are necessary for disturbance-free operation of the useful circuit 2.

[0030] The invention is not restricted to the above exemplary embodiments. Thus, the supply voltage VDD can be compared stepwise with a plurality of predetermined desired values. Each time one of the predetermined desired values is exceeded (a dedicated voltage divider 20 a, 20 b corresponding thereto), one of the plurality of switchable power supply units 17 b is activated or brought to the quiescent state in a staggered manner.

[0031] In order to avoid excessively frequent, rapid connection and disconnection of power supply units 17 b if the supply voltage VDD is near the (or a) desired value, the low-current comparator 19 has a hysteresis in a preferred embodiment (not illustrated), so that oscillations cannot occur. This technique is generally known to the person skilled in the art and, therefore, is not explained any further here.

[0032]FIG. 4 shows the simplest case, in which only one power supply unit 17 b is activated when the desired value is exceeded. Consequently, only one permanently active power supply unit 17 a and one power supply unit 17 b that can be connected in or disconnected are thus illustrated. This is only one example, however. More generally, M of N power supply units 17 b present are activated, so that the rule holds true that N power supply units 17 b are active in the worst case, while only M power supply units 17 b are active in more favorable conditions. In particular, in this case a plurality of power supply units 17 b may be provided below the desired value, while at least one power supply unit 17 b is operated above the desired value. List of reference symbols 1 Integrated circuit 2 Useful circuit of the integrated circuit 3 Power supply unit 4 Lead to useful circuit 5 First external supply line 6 Second external supply line 7 Generator circuit according to the prior art 8 Driver transistor 9 Comparator 10 Voltage divider, 10a first resistor, 10b second resistor 11 Bandgap reference circuit 12 ENABLE transistors, 12a first pFET ENABLE transistor, 12b second nFET ENABLE transistor 13 nFET input transistor, 13a first nEET input transistor, 13b second nFET input transistor 14 Collector resistors (pFET transistors), 14a first collector resistor, 14b second collector resistor 15 Current source (nFET transistor) 16 nFET ENABLE transistor 17 Modified power supply units, 17a permanent power supply unit, 17b switchable power supply unit 18 Control unit 19 Low-current comparator 20 Voltage divider, 20a first resistor, 20b second resistor 

1. Integrated circuit (1), which is supplied externally by a supply voltage (VDD), having at least one useful circuit (2) and a power supply for the at least one useful circuit which comprises a plurality of power supply units (3; 17 a, 17 b), characterized in that the power supply comprises a control unit (18) for comparing the supply voltage (VDD) with a predetermined desired value and for switching one or a plurality of the switchable power supply units (17 b) on or off in a manner dependent on the comparison result.
 2. Integrated circuit according to claim 1, characterized in that the control unit (18) comprises a low-current comparator (19) for comparing the supply voltage with the predetermined desired value.
 3. Integrated circuit according to claim 2, characterized in that the low-current comparator (19) comprises a voltage divider (20 a, 20 b) between the supply voltage (VDD) and ground.
 4. Integrated circuit according to claim 2 or 3, characterized in that the reference voltage (REF) is generated by a bandgap reference circuit (11).
 5. Method for controlling a power supply for an integrated circuit, which is supplied externally by a supply voltage (VDD), having at least one useful circuit (2), the power supply comprising a plurality of power supply units (3; 17 a, 17 b), characterized by the following steps: comparison of the supply voltage (VDD) with a predetermined desired value and switching of one or a plurality of the switchable power supply units (17 b) on or off in a manner dependent on the comparison result by a control unit (18).
 6. Method according to claim 5, characterized in that the comparison of the supply voltage (VDD) is carried out stepwise with a plurality of predetermined desired values, so that the switchable power supply units (17 b) are connected in a staggered manner.
 7. Method according to either of claims 5 and 6, characterized in that the switchable power supply units (17 b) are switched on and off with a hysteresis, thereby preventing oscillations. 